In one process proven to be useful a probe is inserted from above into the soil in a substantially vertical direction and pushed down to the depth required. Thereupon, the soil is abruptly loosened by means of compressed air. Next, the probe is pulled up and reinserted into the soil at a suitable distance. The process of vertically inserting the probe into the soil, pulling it up and reinserting it is repeated until the entire surface, or the soil area to be so treated, has been loosened. Particularly if the area to be treated is extensive, continuous insertion and pulling up of the probe may slow down the flow of operations (cf. German patent No. 27 42 606).